Mono-Phase Motors
Mono-Phase Motors
The structure of 1 phase induction motors consists of two basic components: stator and rotor. Stator forms the fixed part of the motor. Stator contains stator core and field windings. Stators of 1-phase asynchronous motors usually have 2 windings as main and auxiliary windings. The rotor is the rotating part of the motor. The rotors of the ring asynchronous motors have winding, while squirrel-cage induction motors have short-circuited busbars.
In asynchronous motors, the frequency of the rotating field created in the air gap and the rotation frequency of the rotor are not the same. These motors are called asynchronous for this reason. The frequency of the rotating field in the air gap depends on the supply frequency and the number of poles of the motor and does not change with the load of the motor, while the rotation frequency of the rotor changes depending on the load. As the load increases in the working area of the engine, the engine speed decreases, and as the load decreases, the speed increases. The engine speed is highest in idle operation. The number of revolutions of the motor in the motor operating area of the induction motor cannot exceed the revolutions of the rotating field. The number of revolutions of the rotating field is calculated as follows:
N = 120 x f/P
N: Number of revolutions of the rotating field [rpm]
f: Supply frequency [Hz]
P: Number of poles of stator winding
As can be seen from here, the rotating field speed of a 2-pole motor will be 3000rpm and a rotating field speed of a 4-pole motor will be 1500rpm.
In single phase asynchronous motors, alternating currents with different phases from the main and auxiliary winding must pass in order for starting torque to occur. To achieve this, a series capacitor is connected to the auxiliary winding circuit. Thus, a two-phase motor is formed. In addition to the permanent capacitor, in order to increase the starting torque of the motor, a start-up capacitor that will be active only during the start-up period and be deactivated by a mechanism when the start-up is completed can also be used.